1. Field of the Invention
This invention relates to a constant velocity joint, particularly a slide type tripod type constant velocity joint.
2. Brief Description of the Prior Art
Generally, a constant velocity joint is a kind of universal joint adapted to join two shafts, driving side and driven side, and capable of transmitting torque at constant velocity even if there is an angle between said two shafts. The slide type allows a relative axial displacement between two shafts by the plunging of the joint, while the tripod type comprises a tripod member having three radially projecting leg shaft and joined to one shaft, and a hollow cylindrical outer joint member having three axially extending track grooves and joined to the other shaft, the leg shafts of the tripod member being received in the track grooves of the outer joint member to effect torque transmission.
An example of a slide type tripod type constant velocity joint will now be described with reference to FIG. 14. It comprises an outer joint member 1 having three axially extending track grooves 2 formed in the inner peripheral surface thereof, a tripod member 4 inserted in the outer joint member 1 and having three radially projecting leg shafts 5 having annular rollers 7 rotatably fitted on their columnar outer peripheral surfaces through a plurality of needle rollers 6, said rollers 7 being inserted in the track grooves 2. A pair of roller guide surfaces 3 opposed to each other in the circumferential direction of the track groove 2 are concave surface (partial cylindrical surfaces) parallel with the axis of the outer joint member 1, while the outer peripheral surfaces of the rollers 7 fitted on the three leg shafts 5 are convex surfaces (partial sphere surfaces) suited for the roller guide surfaces 3. Each roller 7 is engaged with the roller guide surfaces 3 of the corresponding track groove 2 and is capable of moving axially of the outer joint member 1 along the track groove 2 while rotating around the axis of the leg shaft 5.
As shown in FIG. 14(B), when torque is transmitted with the joint taking an operating angle xcex8, the roller 7 and the roller guide surface 3 are in a mutually crossing relationship, as shown in FIG. 14(C). In this case, whereas the roller 7 tends to make a rolling movement in the direction of arrow t shown in FIG. 14(B), the roller 7 moves while being restrained by the roller guide surface 3 because the roller guide surfaces 3 are partial cylindrical surfaces parallel with the axis of the outer joint member 1. As a result, sliding friction takes place between the roller guide surfaces 3 and the roller 7, producing a slide resistance. Further, this sliding friction produces induced thrust in the axial direction. Such slide resistance and induced thrust cause vibrations and noise in a car body, influencing the NVH (noise, vibration and harshness) of automobiles, decreasing the freedom of the design of the suspension; thus, it is desired to minimize said slide resistance and induced thrust.
As for a slide type tripod type constant velocity joint that is designed to decrease such slide resistance and induced thrust, for example, one having the construction shown in FIG. 15 is known. That is, as shown, the outer peripheral surface of the leg shaft 5 of the tripod member 4 is made a true spherical surface, and slidably fitted on this true spherical surface is the cylindrical inner peripheral surface of a cylindrical ring 8. The ring 8 and roller 7 constitute a roller assembly which is relatively rotatable through needle rollers 6. The needle rollers 6 are disposed in the so-called xe2x80x9call roller conditionxe2x80x9d between the cylindrical outer peripheral surface of the ring 8 and the cylindrical inner peripheral surface of the roller 7 and are prevented from slipping off by annular stop rings 9. The roller 7 is received in the track groove 2 in the outer joint member 1, and is capable of moving axially of the outer joint member 1 while rolling on the roller guide surfaces 3 of the track groove 2.
The outer peripheral surface of the leg shaft 5 is a true spherical surface having a center of curvature on the axis of the leg shaft 5, and the roller assembly (7, 8, 9) oscillates around said center of curvature. The roller assembly is oscillatable; therefore, when torque transmission is effected with the outer joint member 1 and the tripod member 4 taking an operating angle, the roller 7 is guided by roller guide surfaces 3 of the outer joint member 1 to keep a position parallel with the axis of the outer joint member 1, and keeping this position, it correctly rolls on the roller guide surfaces 3. Therefore, the sliding friction produced during torque transmission with the operating angle taken is reduced, suppressing the generation of slide resistance and induced thrust.
It is known to use a slide type tripod type constant velocity joint in order to transmit torque at constant velocity from an automobile engine to the wheels. The slide type tripod type constant velocity joint has barrel shaped rollers attached to the leg shafts of the tripod member and needle rollers are used as xe2x80x9ccageless all roller typexe2x80x9d to serve as rolling elements between the outer peripheral surface of the leg shaft and the inner peripheral surface of the barrel shaped roller. And, when torque is transmitted with an operating angle taken, induced thrust is produced by mutual friction between the inner parts during rotation, and slide resistance is produced even during stoppage if the joint is subjected to forceful axial expansion and contraction. The typical NVH phenomenon of automobiles in which such induced thrust and slide resistance take part includes the rolling of the car body during running, which is connected with the former, and a D-range idling vibration phenomenon in an AT car during stoppage, which is connected with the latter.
The key to solving the automobile NVH problem is to reducing the size of the induced thrust and slide resistance of the joint. Generally, the induced thrust and slide resistance of the joint tend to depend on the size of the operating angle. Therefore, applying the joint to the drive shaft of an automobile leads to a design restriction inhibiting the operating angle from being increased. Thus, in order to increase the freedom of the design of the suspension of automobiles, it has been a problem to reduce and stabilize the induced thrust and slide resistance.
However, since the rolling elements in the conventional slide type tripod type constant velocity joint are needle rollers of the all roller type, unbalanced loads, such as edge load, tend to act on the rolling element surfaces owing to the skewing or the like of the rollers during rotation. Further, the contact state does not become stabilized owing to factors associated with interior clearances and precision, resulting in the barrel shaped rollers being inclined to produce an edge load. Further, because of the construction, relative slip occurs between the ends of the barrel shaped roller, the leg shaft and the stop rings. Such phenomena as skew, edge load and relative slip are believed to govern the size of the frictional force in the joint.
Accordingly, an object of the present invention is to minimize the frictional force to further reduce the induced thrust and slide resistance and to improve stability.
An invention described in claim 1 is a constant velocity joint comprising an outer joint member having three track grooves each having circumferentially opposed roller guide surfaces, a tripod member having three radially projecting leg shafts, a roller inserted in each said track groove, and a ring fitted on each said leg shaft to rotatably support said roller, said roller being movable along said roller guide surfaces axially of the outer joint member, wherein said roller consists of a set of annular roller portions, the inner periphery of each said annular roller portion and the outer periphery of said ring being respectively formed with a raceway surface for a single row of balls to roll thereon, with balls interposed between the raceway surfaces.
The roller consisting of a set of annular roller portions includes not only a first type which consists of two annular roller portions but also a second type which consists of three annular roller portions and a third type having an intermediate body interposed between adjacent annular roller portions. Therefore, in the case of the roller consisting of two annular roller portions, the roller has an outer raceway surface over the two annular roller portions. In the case of the roller consisting of three annular roller portions, the roller has an outer raceway surface over the three annular roller portions or has outer raceway surfaces in the annular roller portions disposed on both sides.
Since the roller is of split construction consisting a set of annular roller portions, relative rotation of the annular roller portions is allowed, thus reducing slide resistance and rolling resistance. That is, when torque is transmitted with the outer joint member and the tripod member taking an operating angle, the roller swings while describing an arc with respect to the roller guide surfaces. At this time, since the position of contact between each annular roller portion and the roller guide surface are spaced axially of the leg shaft, the distance from the position of contact between each annular roller portion and the roller guide surface to the center of the tripod member differs, and the peripheral speeds of both annular roller portions differ from each other. As a result of the peripheral speeds differing from each other, an angular positional deviation of the annular roller portions can take place. However, since the annular roller portions are relatively rotatable, said angular positional deviation is accommodated by the relative rotation of the annular roller portions. Therefore, the slide resistance and rolling resistance associated with the roller arcuately swinging on the roller guide surfaces are reduced. Further, the split construction of the roller facilitates incorporation of balls and eliminates the need to provide an introducing groove.
Since the roller interposed between the tripod member and the outer joint member is supported by balls which always smoothly rotate with low friction without causing any trouble, such as skew, low friction low resistance rolling is realized when the roller rolls in the track groove in the outer joint member along the roller guide surfaces. Therefore, the slide resistance associated with the roller sliding in the track groove axially of the outer joint member, and the induced thrust produced when torque is transmitted with an operating angle formed between the outer joint member and the tripod member, are further reduced; thus, a high-performance slide type tripod type constant velocity joint with reduced noise and vibration can be provided.
Further, supporting the roller by balls ensures that as compared with the case of needle rollers, the load capacity for moment load increases and durability improves. Further, it is believed that it becomes easier for the annular roller portions to rotate synchronously.
The invention described in Claim 2 is a constant velocity joint as set forth in Claim 1, characterized in that said set of annular roller portions abut against each other axially of said leg shaft.
Thus, said set of annular roller portions abutting against each other axially of said leg shaft results in the set of annular roller portions moving as a unit axially of the joint on the roller guide surfaces. Of course, the relative rotation of the annular roller portions, which only abut against each other, is possible, as described above.
The invention described in Claim 3 is a constant velocity joint as set forth in Claim 1, characterized in that said set of annular roller portions has a clearance axially of said leg shaft.
Thus, said set of annular roller portions has a clearance axially of said leg shaft; therefore, even if a dimensional variation between the annular roller portions or between the annular roller portions and the roller guide surfaces of the outer joint member occurs within dimensional tolerance limits, good contact between the two can be secured to allow the roller assembly to move smoothly axially of the joint and on the roller guide surfaces. Further, the lubricating agent readily flows through the clearance between the set of annular roller portions, with the result that the lubricating performance between the roller and the roller guide surfaces is improved to reduce the friction resistance, suppressing heat generation, wear, flaking, adhesion, etc., thus improving the durability of the constant velocity joint.
The invention described in Claim 4 through 6 are a constant velocity joint as set forth in any of Claims 1 through 3, characterized in that the inner peripheral surface of said ring has a convexly arcuate section, and the outer peripheral surface of said leg shaft has a sectional shape such that it contacts the inner peripheral surface of said ring in a direction orthogonal to the axis of the joint and forms a clearance between itself and the inner peripheral surface of said ring in the axial direction of the joint. Concerning the cross sectional shape of the leg shaft, the wording xe2x80x9ca sectional shape such that it contacts the inner peripheral surface of said ring in a direction orthogonal to the axis of the joint and forms a clearance between itself and the inner peripheral surface of said ring in the axial direction of the joint,xe2x80x9d in other words, means a shape such that the surface portions of the tripod member opposed to each other axially of the tripod member recede toward each other, i.e., from an imaginary cylindrical surface toward the smaller diameter side. A concrete example thereof is an elliptic shape (Claims 7 through 9). Herein, it is to be understood that xe2x80x9celliptic shapexe2x80x9d is not limited literally to an ellipse and includes shapes called egg-shape, oval, etc.
Forming the cross sectional shape of the leg shaft as said shape allows the leg shaft to incline with respect to the outer joint member without changing the attitude of the roller assembly when the joint takes an operating angle. Furthermore, as is clear from a comparison between FIGS. 3 and 15(C), since the ellipse of contact between the outer peripheral surface of the leg shaft and the ring approaches a dot from an elongated form, the friction moment tending to incline the roller assembly is reduced. Therefore, the attitude of the roller assembly is stabilized all the time, and the roller is held parallel with the roller guide surfaces, so that the roller can roll smoothly. This contributes to reduction of the slide resistance and to reduction of induced thrust as well. Further, there is another advantage that the increased modulus of section of the root of the leg shaft increases the bending strength of the leg shaft. In addition, it is not necessary that the inner peripheral surface of the ring be cylindrical throughout the length; only the central portion contacting the leg shaft may be cylindrical, and both ends may be formed with flanks to avoid interference when the leg shat is inclined.
The roller assembly is interposed between the leg shaft and the outer joint member to perform the function of transmitting torque. Since the direction of transmission of torque in this type of constant velocity joint is always orthogonal to the axis of joint, transmission of torque is possible in that the leg shaft and the ring are in contact with each other in the direction of transmission of torque. Even if there is a clearance between the two in the axial direction of the joint, there is no possibility of causing trouble to torque transmission.
Furthermore, since the leg shaft is allowed to incline without inclining the ring, the roller is allowed to roll smoothly on the roller guide surfaces without being inclined. Therefore, a flange which is sometimes provided in the track groove in the outer joint member to inhibit the inclination of the roller may be omitted. Omission of such flange makes possible the reduction of weight of the outer joint member and the simplification of processing, and also eliminates the slide resistance due to the sliding contact between the roller and the flange, with the result that further reduction of slide resistance and induced thrust are achieved.
The invention is not limited to the embodiments described above in which the cross section of leg shaft is substantially elliptic. For example, it is applicable to the following arrangement. That is, the inventions described in Claims 10 through 12 are a constant velocity joint as set forth in any of Claims 1 through 3, characterized in that the inner peripheral surface of said ring is cylindrical and the outer peripheral surface of said leg shaft is spherical. The inventions described in Claims 13 through 15 are a constant velocity joint as set forth in any of Claims 1 through 3, characterized in that a bushing whose outer peripheral surface is convexly spherical and whose inner peripheral surface is cylindrical is interposed between the concavely spherical inner peripheral surface of said ring and the cylindrical outer peripheral surface of said leg shaft. The invention described in Claim 16 is a constant velocity joint as set forth in any of Claims 1 through 15, characterized in that the longitudinal section of the outer peripheral surface of said roller is convexly arcuate, and the cross section of said roller guide surfaces is concavely arcuate.
The invention described in Claim 17 is a constant velocity joint as set forth in any of Claims 1 through 15, characterized in that said balls and said raceway surface contact each other with a contact angle. Such arrangement increases the rigidity, serving to increase the load capacity and durability.
The invention described in Claim 18 is a constant velocity joint as set forth in any of Claims 1 through 15, characterized in that said roller and said roller guide surfaces make angular contact with each other. The roller and the roller guide surfaces make angular contact with each other, thereby making it difficult for the roller to swing, so that its attitude becomes further stable; therefore, when moving axially of the outer joint member, the roller smoothly rolls on the roller guide surfaces with less resistance. To give a concrete example of the arrangement to realize such angular contact, the generatrix of the outer peripheral surface of the roller may be convexly arcuate and the sectional shape of the roller guide surfaces may be taper or Gothic arch.